Atmospheric corrosion remains a persistent and evasive challenge to the functional lifetime and performance of structural, decorative, electronic and high-tech materials. See G. Koch et al., International Measures of Prevention, Application, and Economics of Corrosion Technologies Study, NACE International IMPACT Report (2016). Films and coatings have long been used to combat corrosion by physically separating metals from the corrosive medium, or by inhibiting electrochemical reactions that drive corrosion. Ultrathin nanocomposite films fabricated by layer-by-layer (LbL) assembly form an emerging class of coatings with remarkable barrier performance. See M. A. Priolo et al., Nano Lett. 10(12), 4970 (2010); and P. Tzeng et al., J. Memb. Sci. 452, 46 (2014). LbL films are constructed by alternating deposition of complementary components by simple and scalable aqueous dip-coating or spraying processes. The components sequentially bind together with attractive forces (e.g., electrostatic interactions or hydrogen bonding). See J. J. Richardson et al., Chem. Rev. 116(23), 14828 (2016). Adjustments to component solution chemistry and process parameters enable precise control over film composition and architecture. The resulting versatility, conformal nature, gas impermeability, and thinness make LbL films attractive candidates for anti-corrosion coatings. Similarly, recent work has found that polyelectrolyte multilayer films considerably improve corrosion resistance of steel and light alloys by charge and mass transfer inhibition during immersion in salt water solutions, and even demonstrate self-healing properties when constructed with weak, mobile polyelectrolyte layers. See T. R. Farhat et al., Electrochem. Solid-State Lett. 5(4), B13 (2002); D. V. Andreeva et al., ACS Appl. Mater. Interfaces 2(7), 1954 (2010); P. C. Suarez-Martinez et al., Macromol. Mater. Eng. 302, (2017); and E. Faure et al., Langmuir 28(5), 2971 (2012).
Atmospheric corrosion concerns often arise in electronics applications, where thin, conformal and transparent coatings are often desired. Hydrogen sulfide is one of several sulfur-containing gases and air pollutants that are particularly corrosive to copper, with even ppb levels in the air causing breakdown of electronics. See T. Graedel et al., Corr. Sci. 25(12), 1163 (1985). Recent studies have attempted to address atmospheric corrosion of copper using graphene and graphene oxide as gas barriers. See J. Lei et al., ACS Appl. Mater. Interfaces 9(13), 11902 (2017); D. Prasai et al., ACS Nano 6(2), 1102 (2012); M. Schriver et al., ACS Nano 7(7), 5763 (2013); X. Xu et al., Adv. Mater. 30(6), 1702944 (2017); and M. Wang et al., Adv. Mater. 29(47), (2017). While these materials provide short term (hours) corrosion protection at ambient and elevated temperatures, their effectiveness diminishes over time due to infiltration by defects and, with humidity, catalysis of corrosion by the coating itself. See J. Lei et al., ACS Appl. Mater. Interfaces 9(13), 11902 (2017); M. Schriver et al., ACS Nano 7(7), 5763 (2013); and S. Matteucci et al., Transport of Gases and Vapors in Glassy and Rubbery Polymers, In Materials Science of Membranes for Gas and Vapor Separation; Yampolskii, Y.; Pinnau, I.; Freeman, B. D., Eds.; John Wiley & Sons: West Sussex, England, 2006; Chapter 1, pp 1-47.